The Citadel of Montreal was a former fortress used to defend the city.
Smaller than the one in Old Quebec, the Citadel was built by the French in 1690, with a cannon battery added in 1723.
The fort was demolished by the British in 1821 to allow for the extension of Notre-Dame Street.
The Citadel is in this map of Montreal, 1749. Inside the walls, the long rectangle in relief, at north-east corner
See also 
Coordinates: 45°30′42″N 73°33′06″W / 45.51167°N 73.55167°W